A general goal with microfluidic devices is to integrate fluidic functions for as many process steps as possible within the same microchannel structure. Integration is beneficial since it reduces time-consuming sample transfer operations as well as the risk for loss of samples and reagents, for instance. Integration may lead to a need for excluding liquids containing components that negatively affect downstream steps from the main process stream. Typical such liquids are washing liquids that may contain contaminants, and liquids that require separate processing. One way of doing this is to withdraw this kind of liquids from the main process stream/flow path of a microchannel structure. This requires simple and reliable liquid routers.
Another general goal with microfluidic devices is to perform a given process protocol with a high degree of parallelism, i.e. to have a large number of similar microchannel structures on the same device. A liquid routing function thus must be easy to reproduce between the microchannel structures.
Routing functions based on an inlet microconduit that branches into two daughter/exit microconduits and where the routing depends on a difference in surface characteristics between the daughter microconduits have previously been described in the context of centrifugally based microfluidic devices: a general description has been given in WO 02074438 (Gyros AB), which is incorporated herein by reference in its entirety; a router comprising an outwardly directed inlet microconduit, an outwardly directed exit microconduit, possible with a hydrophobized section immediately downstream the branching, and an inwardly directed exit microconduit is described in WO 0040750 (Gyros AB), WO 0147638 (Gyros AB), WO 0146465 (Gyros AB), WO 02074438 (Gyros AB), each of which is incorporated herein by reference in its entirety. A router comprising two outwardly directed exit microconduits with no discussion about any difference in inner surface characteristics is described in WO 0147638 (Gyros AB). See also WO 9958245 (Gyros AB), each of which is incorporated herein by reference in its entirety.
Branched inlet microconduits have also been used in volume-defining units where one of the branches leads into a volume-metering microcavity and the other branch is an overflow microconduit leading to a waste reservoir or waste opening. See WO 02075775 (Gyros AB), WO 02075776 (Gyros AB), WO 02074438 (Gyros AB), WO 03018198 (Gyros AB), each of which is incorporated herein by reference in its entirety. This kind of units has not been used for liquid routing in which the liquid flow specifically goes into only one of the branches and then is switched to the other branch by increasing the force acting on the liquid.
It now has been recognized that there is a general need for improvements with respect to the possibility to freely switch back and forth between the exit microconduits of a liquid router in a controlled and regulated manner without the need of electricity, movable parts etc on the device. Thus a main object is to provide reliable routing functions for centrifugally based microfluidic devices in which a simple change in spin speed will determine into which particular exit microconduit the liquid will be directed. The length of the period of time for spinning at the particular speed should determine the amount of liquid transferred to the particular exit microconduit. A subobject is to provide liquid routers in which one can easily switch between two exit microconduits one, two, three or more times, e.g. back and forth one, two, three or more times between the exit microconduits.
Further a liquid router between two process microcavities should be robust and reliable such that two, three or more microchannel structures individually comprising the router could be run in parallel.